The present invention relates to a multi purpose hoisting device, according to the preamble of claim 1. The present invention also relates to a method for lowering an object to a deepwater installation site.
A second aspect of the invention relates to a hoisting device comprising a heave compensation mechanism, according to the preamble of claim 19.
Multi purpose hoisting devices are known from the art, and are typically used on a drilling vessels, pipe laying vessels and production platforms.
For example, WO 02/18742 discloses a drilling mast, also referred to as multi purpose tower. Such a drilling mast is typically mounted on a drilling vessel, for drilling in the seabed, for example for oil or gas. This particular drilling mast is at its top side provided with first and second hoisting device in a first and second firing line, for manipulating objects, such as a drill string, in the longitudinal direction of the mast.
Drilling from a vessel is carried out with a drilling tool fixed on the end of a drill string. The drill string is supported by one of the hoisting mechanisms, more in particular by a trolley which is movably connected to the drilling mast and supported by a hoisting cable.
Each of the hoisting mechanisms is provided with a heave compensation system. Such heave compensation systems are generally known. A heave compensation system is used to compensate for the movements that the ship makes relative to the seabed, as a result of wind, swell and the like. With the heave compensation system, the hoisting mechanism can keep the position of the trolley, and thus the end of the drill string, substantially constant relative to the seabed during the assembly of the drilling mast, or during the drilling.
Besides manipulating objects such as drill strings, with off shore exploration there is also the need for lifting and lowering objects, such as blow out preventers (BOP), BOP stack modules, X-mas trees and subsea manifolds, to and from deepwater installation sites.
For this purpose, the vessel can be provided with a deepwater hoisting crane comprising a deepwater hoisting mechanism. However, an extra crane requires extra deck space, which is limited on a floating vessel. Furthermore, the crane adds extra weight to the vessel.